Ultrasound images are generally provided in gray scale, and physicians and medical technicians tend to prefer viewing ultrasound images in gray scale as opposed to in color. The gray scale images provide for enhanced resolution of the image by providing sharpened contrasts between black and white and varying shades of gray. The gray scale image may assist a user studying the image to ascertain problems or identify features that the user might not identify if the image did not have enhanced resolution. The display technology currently in use for viewing ultrasound images utilizes a color display, such as a liquid crystal display (LCD), because some ultrasound imaging techniques, such as Doppler, require the use of color. However, when an image is rendered in gray scale on a color display, there will only be a certain number of gray levels available to represent the image, and thus, resolution and clarity may be lost as the image is mapped to these gray levels for display.
Some color displays limit the number of grays that a user can view on the display to approximately 64 different levels of gray; however, the human eye can typically see about 256 different levels of gray. Due to the display limits, for an image to be displayed, mapping would occur to convert image data from a higher gray resolution into the 64 shades of gray that could be displayed. As shown in the table in FIG. 1, the goal intensity may range from 0 to 255; however, the goal intensity could only be mapped to actual intensities ranging from 0 to 63. Even though the viewer would be able to detect 256 levels of gray, the viewer would only see the 64 different levels of gray actually displayed on the screen, resulting in images that would not have the smoother contrast that would be desired.
Further, when mapping of this sort is used to view gray scale images on a color display, the images that result may have a blotchy-looking appearance. When the image that results loses it clarity and resolution, it would not be an ideal for a doctor or other medical technicians, for example, to analyze and interpret because he/she would be less likely to detect variations between the different gray levels.
Another method proposed for creating better gray scale images on a color display was to transition from image to image in a temporal sense. In making this transition, one image could be illuminated at one gray level, and the next image might be illuminated at a slightly different gray level. Due to the temporal positioning of the images relative to one another, the eye then might perceive intermediate gray levels between the gray levels associated with each of the images. This method reduces the effective frame rate by 2 and might appear to flicker to the viewer. The method does not ensure that a sufficient number of gray levels are displayed nor does it ensure that a smooth transition between gray intensities might be achieved.
Thus, there is a need to enhance the gray level output on a color display. Such an enhancement may provide a smoother transition between gray intensity levels on the color display and improve the clarity and resolution of the images displayed in gray scale.